Reusable hose end fittings normally have a stem portion which locates within the bore of the hose end and a ferrule portion which locates about the hose end, the ferrule portion being screw-coupled to the stem portion. During attachment of the end fitting to the hose, the hose end is located within the ferrule portion (with or without the outer covering of the hose end being pared to reveal and wire reinforcement) and the stem portion is then moved into the hose bore so that the hose wall is clamped between the stem and ferrule portions. Movement of the stem portion into the ferrule portion is effected by engaging male and female thread portions of the stem and ferrule portions respectively and by screwing the stem portion relative to the ferrule portion so that it is advanced in an axial direction into the ferrule portion. Considerable torque must be applied to the stem portion to effect the screwing operation, in order to overcome frictional and other forces which are exerted on the stem portion by the wall of the hose as it is being clamped between the stem and ferrule portions.
In order to facilitate insertion of the stem portion into the hose bore (whilst the wall of the hose is being clamped between the stem and ferrule portions) many hose end fittings have a stem portion which includes a tapered stem, the taper converging toward the free end of the stem portion which is first inserted into the hose bore and the taper having a substantially constant angle along its length. Thus, as the stem is forced into the bore of the hose, the hose wall is caused to flare outwardly and, as a consequence, the ferrule exerts a clamping (i.e., wedging and deforming) force on the hose wall. The forces exerted on the hose wall affect the torque required to advance the stem into the hose bore, and considerable torque must be applied (particularly in the case of large diameter wire-reinforced hoses) in order to overcome frictional resistance between the stem and the hose bore. The torque requirement increases with increasing advancement of the stem, due to the constantly increasing diameter of the tapered portion of the stem.
Some existing hose end fittings have tapered stems which are formed along a portion of their lengths with barbs or screw threads to aid gripping of the fitted hose end and to resist tensile detachment of the hose from the fitting. However in such cases the stems do have a substantially constant taper angle (embracing the crests of the barbs or screw-threads) and the above observations still apply.